This invention relates to a hot press device for manufacturing a laminated structure, and more particularly to a hot press device for manufacturing a substrate of a printed circuit board. Still more particularly, the present invention relates to a hot press comprising a position detecting means for changing an elevating speed of a heating plate of the hot press from a high speed to a low speed immediately before clamping a plate to be treated; and in the pressure control of the hot press, an accurate pressure control is conducted during clamping at a low pressure.
The hot press device clamps a plurality of heating plates by way of elevating a ram of a clamping cylinder, while the intervals between heating plates are enlarged by lowering the ram. The plates which have been hot-pressed can be taken out by way of this enlargement of the intervals between the heating plates.
The elevating speed of the ram will now be described. Although this speed is preferably to be high for the purpose of shortening the time which is required to complete the work, high speed elevating of the ram after the clamping has started deteriorates the quality of a product because the adhesive which is interposed between layers of the laminates to be treated has not been sufficiently melted.
In order to overcome aforesaid problem, the conventional device adopts an arrangement as shown in FIG. 5. Namely, a limit switch supporting rod 103 is suspended from a side surface 101 of a top plate 100 of the hot press through a bracket 102. A limit switch 104 can be adapted to be secured to any desired portion of the aforesaid limit switch supporting rod 103. One end of a bracket 106 is secured to a side surface of a top heating plate 105 which moves vertically, while a cam 107 is secured to another end so as to energize the limit switch 104 by means of this cam 107. Heating plate 109 is fixedly secured to insulating plate 108, which is fixedly secured to plate 100. When the top heating plate of the hot press which moves vertically has come up to a predetermined position, a signal is generated so as to change the elevating speed of the heating plate to a low speed.
However, in the aforesaid mechanism, it is needed to adjust the position of the limit switch 104 along the limit switch supporting rod 103 so as to shift the position at which the elevating speed of the heating plate is changed to low, whenever the thickness of the plate to be treated is changed.
This hampers automation of preparatory work in a hot press device. Furthermore, such a position adjustment is very difficult in a vacuum hot press in which the outer circumference of the hot press is closed.
The change of the speed of the ram will now be described.
The speed of the ram is needed to be changed when the clamping of the heating plates starts as mentioned above.
The way to control the elevation of the ram is changed from the speed control mode to the pressure control mode.
That is, a hydraulic pressure in the clamping cylinder is adjusted by means of a pressure control valve so as to vary the pressure (kg/cm.sup.2) which is applied to the plate to be hot-pressed, in accordance with a melting condition of a prepreg for the plate to be hot-pressed. However, the characteristics of the pressure control valve which is used for adjusting the pressure is very unstable when it is used in a low pressure range of substantially 0 kg/cm.sup.2 to 10 kg/cm.sup.2
For example, when a hot press provided with a single action clamping cylinder 30 shown in FIG. 6 is used, oil is led to flow into the clamping cylinder 30 by a pump for the purpose of elevating a ram 30a. When low pressure control is carried out for the purpose of adjusting the hydraulic pressure in the clamping cylinder 30 by means of the pressure control valve, the only possible way to be employed is to set the pressure control valve to operate at low pressure. However, as mentioned above, it is difficult for the pressure control valve to accurately control the pressure in a low pressure region. When press-forming a product of a thin thickness, it is required to clamp it with low pressure which meets the fusing degree of a prepreg of the product.